The present application relates to a data storage system, more particularly to a storage system for performing remote copies to multiple sites.
Industry and commerce have become so dependent on computer systems with online or interactive applications that an interruption of only a few minutes in the availability of those applications can have serious financial consequences. Outages of more than a few hours can sometimes threaten a company's or an institution's existence. In some cases, regulatory requirements can impose fines or other penalties for disruptions or delays in services that are caused by application outages.
As a consequence of this growing intolerance for application outages, there is a keen interest in improving the availability of these applications during normal operations and in decreasing the amount of time needed to recover from equipment failure or other disastrous situations.
In addition to these brief interruptions in normal operations, precautions must be taken for longer-duration outages caused by disasters such as equipment or software failure, fire, flood, earthquake, airplane crashes, terrorist or vandal activities. Realistically, these outages cannot be avoided entirely but the probability of an extended outage can be reduced to an arbitrarily small value by implementing complex systems of geographically dispersed components with redundant features that have no single point of failure.
The exposure to an extended outage can be mitigated by providing a secondary site for storing redundant or back-up data, as disclosed in U.S. Pat. No. 6,539,462, which is incorporated by reference. The data back-up can be made by performing remote data copy or local data copy (shadow copy) methods. Examples of remote copy and shadow copy are “Truecopy” and “ShadowImage” performed by some of Hitachi storage devices.
Generally a data storage center includes a primary storage site and a secondary storage site. The secondary storage site keeps a copy of production data of primary storage systems at a primary site to increase redundancy. The primary site serves as a production site and contains primary hosts and primary storage systems, and the secondly site serves as a standby and contains secondary hosts and secondary storage systems. The production data are copied from the primary storage systems to the secondly storage systems.
Recently, more and more businesses need to copy data to multiple storage systems at multiple sites to enhance redundancy and data availability. Some businesses are afraid of losing data kept in not only the primary site but also that stored in the secondary site at the same time, particularly if the business has both primary and secondary storage systems within close proximity of each other, e.g., within the same building. Accordingly, some businesses are interested in having a data storage system that has three or more storage sites for multiple data redundancies at these sites to avoid permanent loss of data as a result of a regional disaster.
In addition to their use in disaster recovery, the data redundancies may be used to provide greater data availability to users, e.g., global data sharing. Businesses or enterprises have several sites that are geographically separated that perform separate information processing operations. These enterprises, however, may wish to share data between these multiple sites. For example, master data of products information are managed and updated at the headquarter site, which are distributed to local sites for read only access, thereby providing quicker data access to users. Accordingly, global data sharing is commonly used for enterprise data warehousing.
One type of remote copy technology is a point in time (PiT) remote copy technology that enables users to have a point in time data copy of the primary site at the secondary site. That is, the data stored at the primary site is copied to the secondary site, so that the secondary site mirrors the data content of the primary site at a given instant of time.
The PiT technology is useful for providing data consistency or time consistent data among multiple storage systems at the secondary site. The requirement of keeping data consistency among multiple storage systems is common in disaster recovery for both a very large application that issue input and output requests (IOs) to several storage systems at the same time and a group of applications related to each other that requires data consistency among each of data applications. The PiT technology is also used for global data sharing, which requires data consistency among multiple storage systems, so that distributed applications may refer to the time consistent image.
However, conventional remote copy technologies are designed to provide remote copy between only two sites. Even if these technologies are extended to support three or more sites, it is difficult to keep data consistency among multiple storage systems without a new technology.